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August 27, 2003: These two images, taken 11 hours apart with NASA's Hubble Space Telescope, reveal two nearly opposite sides of Mars. Hubble snapped these photos as the red planet was making its closest approach to Earth in almost 60,000 years. Mars completed nearly one half a rotation between the two observations.

Q & A: Understanding the Discovery

1. 1. Why does Mars have a rusty orange color?




The planet's surface is colored by iron oxide.

2. 2. Does the planet have seasons?




Mars has seasonal changes because it is tilted, like Earth. But each season is twice as long as Earth's because it takes twice as long for Mars to orbit the Sun.

3. 3. What are the polar ice caps made of?




The northern and southern polar ice caps are made of a mixture of water ice and solid carbon dioxide.

4. 4. Are the Martian volcanoes active?




The volcanoes were active long ago, but the red planet's core has cooled. The volcanoes, therefore, have no heat to power them.

5. 5. What is the difference in the terrain between the northern and southern hemispheres?




The southern part of Mars consists mostly of ancient, heavily cratered terrain. The major impact basins—Hellas, Argyre and Isidis—are located in this hemisphere. The southern landscape is higher than in the north. By contrast, the north's terrain is smoother and more sparsely cratered. The highest areas are the volcanic regions of Tharsis and Elysium.

6. 6. What causes the dust storms?




The global dust storms seem to erupt when Mars is close to the Sun. These immense storms ravage the red planet about every two years. In 2001, the Hubble telescope witnessed the biggest global dust storm seen on Mars in several decades. The Martian dust storm, larger by far than any seen on Earth, raised a cloud of dust that engulfed the entire planet for several months.

7. 7. Did life ever exist on Mars?




Scientists don't know. But Mars is a terrestrial planet, just like Earth. Rivers, lakes, and maybe even oceans existed on Mars hundred of millions of years ago. Now, however, Mars is too cold and dry, and its atmosphere is too thin to support life as we know it on its surface. Water still could exist underground, but it is no longer detectable on the planet's surface.